Method for producing a three-dimensional circuit arrangement

ABSTRACT

A substrate wafer having components (13) is bonded onto a mount (3) and is thinned from the rear side. After producing a photoresist mask on the rear side of the substrate wafer, the latter is separated in an etching process into individual components (13). After removal of the photoresist mask, a further component (6), in particular a component stack, is applied onto at least one of the individual components (13) and is firmly connected to the individual component (13a).

BACKGROUND OF THE INVENTION

Three-dimensional circuit arrangements are implemented as a componentstack for cubic integration. Individual components are stacked one abovethe other in a component stack, and are firmly connected to one another.In this case, the individual components in each case comprise integratedcircuits, sensor-actuator arrangements and/or passive components. Theindividual components can in this case be produced using differenttechnologies. The various components are electrically connected to oneanother, one above the other, by vertical contacts.

During the production of such a three-dimensional circuit arrangement,the components are first of all produced in a conventional manner in asubstrate. There are then in principle two options for joining thecomponent stack together. On the one hand, the components can all firstof all be separated and then joined together to form the stack. As arule, this is done such that a substrate which comprises a furthercomponent to be added to the stack is bonded by the front side onto arobust mount. The substrate is thinned to about 10 μm from the rearside. The substrate is then separated into the individual components.The separate component is then placed onto a component or a componentstack. The fitted component is mechanically and electrically connectedto the component or the component stack. The component stack formed inthis way is detached from the mount and is connected to furthercomponents in an analogous manner.

On the other hand, the substrate, which comprises a component which isto be added to a stack, is not separated until after mechanicalattachment. To this end, the substrate is bonded by the front side ontoa mount and is thinned from the rear side. The component or thecomponent stack is then placed upside-down onto the substrate and ismechanically and electrically connected to it. The separation intoindividual component stacks does not take place until then.

The separation of substrates into individual components is carried outin microelectronics by sawing. In the case of the first method, thesawing of the substrate is carried out immediately before the componentsare fitted. Contamination, which is produced during sawing of thesubstrate, must be removed from the surface of the components beforemechanical connection.

If the components are mechanically connected to one another with the aidof an adhesive, then, as a rule, the adhesive is applied beforeseparation. After cleaning contamination which has been produced duringsawing, the surface of the adhesive must then be reactivated.

Furthermore, the mount must also be split during separation of thesubstrate. The material of the mount must therefore be selected suchthat it can be separated using the same saw as the thinned substratewafer. Furthermore, in this case, the mount is destroyed when eachcomponent level is added.

In the case of the second method, the separation of the substrate is notcarried out until after the mechanical connection to the component stackwhich is to be added to. The mount must likewise be split in this casewhen the substrate is split. The material for the mount must thereforelikewise be matched to the substrate material. Since component stacksare in this case arranged on the substrate which are each composed ofthinned layers and are highly susceptible to fracture, it is necessaryto avoid the saw touching the edge of the stack. During each step, it istherefore necessary to maintain a minimum distance between the saw edgeand the stack edge. In consequence, the space utilization on thesubstrate and thus the material utilization of the substrate and of themount are limited. A new mount must also be used in this case for eachcomponent level to be added, since this mount is split up duringseparation.

SUMMARY OF THE INVENTION

The invention is based on the problem of specifying a further method forproducing a three-dimensional circuit arrangement, in whichfragmentation of thinned substrate wafers is avoided. In particular, itis intended to achieve better material utilization of the substrate andmount.

In general terms the present invention is a method for producing athree-dimensional circuit arrangement. A substrate wafer which hascomponents in a first main surface is bonded by the first main surfacevia an adhesive layer to a mount. The substrate wafer is thinned from asecond main surface which is opposite the first surface. A photoresistmask is produced on the second main surface. The substrate wafer isseparated in an etching process into individual components which areconnected to the mount. After removal of the photoresist mask, at leastone further component is arranged on at least one of the individualcomponents and is firmly connected thereto to form a component stack.

As the further component, a stacked is fitted which has at least twocomponents which are stacked one above the other and which are firmlyconnected to one another.

The photoresist mask is produced by spin-on deposition of a photoresistlayer, by exposure of the photoresist layer using lithography which isadjusted to the components, and by development of the photoresist layer.

The etching process for separating the substrate wafer is carried out bywet-chemical means.

The etching process for separating the substrate wafer is carried out bya plasma etching process.

The component stack is separated from the mount. The mount isUV-permeable. The adhesive layer is embrittled by UV radiation in orderto detach the component stack from the mount. The mount is formed fromquartz glass, and the adhesive layer is formed from fusion adhesive.

In the method according to the invention, a substrate wafer whichcomprises components in a first main surface is bonded by the first mainsurface onto a mount. The substrate wafer is thinned from a second mainsurface, which is opposite the first. A photoresist mask is thenproduced on the second main surface and is used as an etching mask in asubsequent etching process. The substrate wafer is separated intoindividual components in the etching process. The components arefurthermore connected to the mount via the adhesive layer. Thephotoresist mask is produced such that it protects those areas of thesubstrate wafer in which components are arranged against etching attack.After removal of the photoresist mask, at least one further component isarranged on at least one of the individual components and is firmlyconnected to it to form a component stack. The further component can inthis case itself be a component stack. Since the substrate wafer issplit in an etching process, fragmentation of the substrate wafer, asoccurs during sawing, is reliably avoided.

Since only the substrate wafer itself is split during separation of thesubstrate wafer in the method according to the invention, the materialfor the mount may be chosen as required. The complete component stackcan then be separated by sawing of the mount.

According to another, particularly advantageous embodiment, thecomponent stack is detached from the entire mount. The mount is notdestroyed in this case, so that relatively expensive materials such asceramics, for example, can also be used for the mount. In particular, itis within the scope of the invention to provide the mount from aUV-permeable material, for example quartz glass, and to embrittle, andthus to detach the adhesive layer by UV radiation through the mount, inorder to detach the complete component stack from the mount. If thecomponent stack is detached using a solvent, then this acts betweenadjacent component stacks via the cracks which are opened in the etchingprocess.

The separation of substrate wafers, which comprise integrated circuits,in an anisotropic etching process has admittedly already been proposedin German reference DE 43 08 705 A1, in order to produce chips of anydesired shape which cannot be implemented by a sawing method. Theproblem of fragmentation of thinned substrate wafers and of materialconsumption for cubic integration has not, however, been addressedthere.

Since the substrate wafer thickness is preferably 5 μm to 20 μm afterthinning, the etching process for separation of the substrate wafer canbe carried out both by wet-chemical means and as a plasma etchingprocess. During wet-chemical etching, lateral etching occurs in theorder of magnitude of the substrate wafer thickness which is, forexample, about 10 μm. The distance between adjacent components of thesubstrate wafer must be selected to be appropriately large in the caseof wet-chemical etching. Normal distances between the components on asubstrate wafer using silicon technology are 100 μm, so that the layerthickness of 10 μm does not represent a limitation in this regard.Increased cleanliness can be ensured in the case of a silicon wafer byusing a plasma etching process to separate the substrate wafer. However,this increases the etching time.

It is within the scope of the invention to produce the photoresist maskby spin-on deposition of a photoresist layer onto the second mainsurface, exposure of the photoresist layer using lithography which isadjusted to the components, and development of the photoresist layer.The adjustment of the lithography can be carried out, in particular,onto the visible contact surfaces.

The connection between the components in the component stack can beproduced both with the aid of adhesive, for example fusion adhesive orpolyimide, as well as by soldering of metal surfaces which are appliedto the boundary surfaces.

After the substrate wafer has been ground thin from the second mainsurface, further rear-side processes can first of all be carried out,such as opening of contact holes from the second main surface, forexample, which contact holes extend to wiring planes of the components,and via which electrical contact is made between components which areadjacent in the stack.

The method can be applied particularly advantageously when usingcomponents which are implemented in semiconductor substrates since, inthe case of semiconductor substrates, there is a particularly high riskof fragmentation during processing with separating saws.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel,are set forth with particularity in the appended claims. The invention,together with further objects and advantages, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings, in the several Figures of which like referencenumerals identify like elements, and in which:

FIG. 1 shows a mount having a thinned substrate wafer and a photoresistmask.

FIG. 2 shows the substrate wafer after separation into individualcomponents and after fitting a component stack.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A substrate wafer 1 which is composed, for example, of monocrystallinesilicon and comprises components in the region of a first main surface11 is bonded onto a mount 3 with the aid of an adhesive layer 2. Thecomponents which surround the substrate wafer 1 in the region of thefirst main surface 11, and which are not illustrated in detail for thesake of clarity, comprise integrated circuits and/or sensor and actuatorstructures. The mount 3 is composed, for example, of quartz glass.Fusion adhesive is used, for example, as the adhesive layer 2.

The substrate wafer 1 is thinned, for example by being ground thin, froma second main surface 12 which is opposite the first main surface 11.After thinning, the substrate wafer 1 has a thickness of 5 to 20 μm,preferably 10 μm, at right angles to the first main surface 11. Aphotoresist mask 4 is subsequently applied onto the second main surface12 (see FIG. 1).

The photoresist mask 4 is preferably produced by spin-on deposition of aphotoresist layer onto the second main surface 12 of the substrate wafer1, exposure of the photoresist layer using lithography which is adjustedto the components, and development of the photoresist layer. Thephotoresist mask 4 covers those areas of the second main surface 12 ofthe substrate wafer 1 under which components are arranged. Thephotoresist mask 4 has openings 41 in the substrate wafer 1, betweenadjacent components.

The substrate wafer 1 is now split into individual components 13 in anetching process, for example wet-chemically using etching solutions on achromate/hydrochloric acid base according to Secco or Schimmel (see FIG.2). Alternatively, a plasma etching process is used as the etchingprocess. Reactive ion etching (RIE) with chlorine gas is particularlysuitable, since this is optimized with respect to impurities and etchingduration.

The substrate wafer 1 is cut through completely in the etching process,and the etching process is not interrupted until at least the surface ofthe adhesive layer 2 is exposed.

After removal of the photoresist mask 4, an adhesion layer 5 is appliedto at least one component 13a of the components 13, and a furthercomponent 6 is fitted onto this adhesion layer 5. The further component6 is firmly connected via the adhesion layer 5 to the first-mentionedcomponent 13a. A polyimide layer is suitable, for example, as theadhesion layer 5, or a solder metal layer which forms a permanentmechanical connection via metal surfaces, which are applied on theboundary surfaces of the components 13a and 6, in a soldering step.

The further component 6, as a component stack, may comprise a pluralityof components which are mechanically and electrically connected to oneanother. The component stack, which is formed from the component 13a anda further component 6, is firmly connected to the mount 3, as before,via the adhesive layer 2. The component stack 13a, 6 is removed from themount 3 by detaching the adhesive layer 2.

The adhesive layer 2 is preferably detached by irradiation with UV lighton the rear side, during which the adhesive layer 2 is embrittled. To dothis, it is necessary for the mount 3 to be UV-permeable.

Alternatively, the adhesive layer 2 is dissolved with the aid of asolvent, preferably acetone.

In the practical implementation of the method according to theinvention, it is advantageous to apply an adhesion layer 5, on whichcomponents or a component stack 6 are arranged, simultaneously onto allthe functional components 13. After the mechanical connection of thecomponent stacks which are produced in this way, these stacks aresimultaneously removed from the mount 3 by detaching the adhesive layer2, for example by UV radiation.

The mount 3 is not damaged in the method according to the invention andit is possible to continue using it for fitting further component levelsonto the component stack.

The invention is not limited to the particular details of the methoddepicted and other modifications and applications are contemplated.Certain other changes may be made in the above described method withoutdeparting from the true spirit and scope of the invention hereininvolved. It is intended, therefore, that the subject matter in theabove depiction shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A method for producing a three-dimensionalcircuit arrangement, comprising the steps of:providing a substrate waferhaving components in a first main surface thereof, the substrate waferalso having a second main surface opposite the first main circuit;bonding the first main surface via an adhesive layer to a mount;thinning the substrate wafer from the second main surface; producing aphotoresist mask on the second main surface; separating the substratewafer in an etching process into individual components which areconnected to the mount; and arranging, after removal of the photoresistmask, at least one further component on at least one of the individualcomponents and firmly connecting the at least one further component tothe at least one of the individual components to form a component stack.2. The method as claimed in claim 1, wherein the further component is astack having at least two components which are stacked one above theother and firmly connected to one another.
 3. The method as claimed inclaim 1, wherein the method further comprises producing the photoresistmask by spin-on deposition of a photoresist layer, exposure of thephotoresist layer using lithography which is adjusted to the components,and development of the photoresist layer.
 4. The method as claimed inclaim 1, wherein the etching process for separating the substrate waferis carried out by a wet-chemical process.
 5. The method as claimed inclaim 1, wherein the etching process for separating the substrate waferis carried out by a plasma etching process.
 6. The method as claimed inclaim 1, wherein the method further comprises separating the componentstack from the mount.
 7. The method according to claim 6, wherein themount is UV-permeable, and wherein the method further comprisesembrittling the adhesive layer by UV radiation in order to detach thecomponent stack from the mount.
 8. The method according to claim 7,wherein the mount is formed from quartz glass, and the adhesive layer isformed from fusion adhesive.